Step 1: make sure the controller is actually a potentiometerWe can test this by examining the controller, it is quite easy on this controller, because on the 2 sides we see 2 potentiometers. Its easy to see here that there's potentiometers in this controller. You can see the 3 wires attached to them:
(http://forum.shipsim.com/Uploads/control4.JPG)